Monday, August 26, 2013

Many months ago, we talked about the development of the percussion lock. This was where the idea of striking a shock-sensitive substance with a hammer to ignite the main charge of propellant was originally developed. In that article, we had mentioned that mercury fulminate was originally used as the primer and was later replaced by potassium chlorate. This idea of using a shock sensitive priming material is still used in today's centerfire cartridges. However, there were some issues with using such primer materials and we'll study about them in this post.

In our discussion about the percussion lock previously, we'd mentioned that the inventor (the Rev. Alexander Forsyth) had used mercury fulminates to set off the main charge. Mercury fulminates continued to be used in priming caps for early centerfire cartridges as well, into the end of the 19th century. However, when people started to switch to using smokeless powders, they began to discover the downsides of mercury fulminate. One of the issues was that mercury fulminate tended to degrade when kept in storage. This was not really an issue when using black powder cartridges, because black powder ignites a lot easier than smokeless powders. However, once people started to switch to smokeless powders for extra power, they found that keeping the cartridges in storage would cause the mercury fulminate primers to degrade so much that they could not reliably ignite the smokeless powder, causing misfires and hang fires. One more problem with mercury fulminates was that in conjunction with smokeless powders, it tended to form copper and zinc amalgams in the brass cases of cartridges, thereby making them unsuitable for reloading.

Due to this, the US Army switched to using potassium chlorate primers in 1898. Some other manufacturers used sodium chlorate instead. While these primers did not degrade as much as mercury fulminate, there were some other problems that came with them. When fired, these primers would decompose and leave a residue of potassium chloride (or sodium chloride) behind in the barrel. Those of you who remember your chemistry lessons in school might remember that sodium chloride is the scientific name for common salt. Potassium chloride is also another corrosive salt. These salts are highly hygroscopic (i.e.) they tend to attract water, especially when in humid conditions. Guess what happens when you have salt and water applied to an iron or steel surface -- that's right, it rusts. Therefore, if the barrel and action are not cleaned after firing such cartridges, there's a good chance that they could rust soon after. Swabbing the surfaces with oil will not prevent these salts from attracting water and rusting the metal.

As a result of this, primers using non-corrosive chemicals were developed in the 1920s, but these were generally used in civilian ammunition only, as the early non-corrosive primers did not last as well in storage as corrosive primers. Due to this, military ammunition tended to use corrosive primers and this was indeed the case for US military ammunition until the 1950s or so. Some other countries (e.g. former Soviet Union, China, Yugoslavia, Bulgaria etc.) continued to use corrosive primers in their cartridges for much longer than this, well into the 1970s and 1980s. Therefore, depending on the source and the age of the ammunition, the user must be wary lest the ammunition is corrosive.

So how does a user ensure that his firearm doesn't rust after using corrosive ammunition. The good news is that this is fairly easy to handle. It turns out that these corrosive salts dissolve in water. Therefore, cleaning the firearm thoroughly using water or a water based lubricant should do the trick. Some people use hot soapy water, others use plain water, still others swear by windex glass cleaner (which is largely water based). After washing off the residue, the firearm should then be dried, then cleaned with normal bore cleaning solution and oiled, as per the normal cleaning procedures.

The firearm should be thoroughly cleaned as soon as possible after firing the corrosive ammunition, to ensure that the corrosive chemicals are removed before they can damage the firearm. While this may seem like a bit of extra work, it is well worth it because there is no way to restore a barrel or chamber back to perfect condition, once it has started to rust. Therefore, the user should go through the extra effort if the ammunition is suspected to use corrosive primers.

As it turns out, the price of surplus ammunition using corrosive primers is often much lower than other types and it is also widely available in the market. So how does a user identify if the ammunition is corrosive or not? One way is by looking at the markings on the cartridges and the manufacturer of the ammunition. For instance, if it is surplus ammunition from certain countries such as the former Soviet Union, Yugoslavia or China, there is a good chance it uses corrosive primers, especially if it is manufactured before the 1980s. US-made ammunition has markings that can give a good clue as to whether the primers are corrosive or not. In case of doubt, there's an easy way to find this out. The user can take a cartridge, pull out the bullet from the front and empty out the powder from the cartridge and only leave the primer behind. Then. the user fires the empty cartridge onto a mild steel plate from a distance of about 1 inch from the muzzle, so that the primer chemicals are deposited on the plate. The user also fires another primer that is known to be non-corrosive onto another section of the steel plate. After firing the two cartridges, the user cleans the firearm as detailed in the procedure above, in case the suspect ammo is indeed corrosive. Then the user simply keeps the steel plate in a warm humid area for a few days. If the section where the suspect primer is fired over shows substantial rusting, then it uses corrosive chemicals.

Another way is to use bright common nails (which are nails made of mild steel with no coating) and pop a primers over one of these nails. If the nail rusts within a couple of days, then the primer is corrosive. The following video shows how this is done, using simple household tools:

Interestingly, the box of suspect ammunition actually says that it is non-corrosive on the box, but it turns out to be corrosive after all. Happy viewing!

Monday, August 19, 2013

Imagine you are now the proud owner of a classic Russian Mosin-Nagant M-91 rifle and are excited to try it out for the first time. So you take it out to the range, adjust the iron sights for a target 400 meters away and shoot at it. Upon shooting a few times, you examine the target and notice that you're not hitting where you're aiming at. Is there something wrong with the rifle? Actually, the answer may have to do with your misunderstanding about how the sight works.

A Konovalov type Mosin-Nagant adjustable iron sight.

In the above image, we see a Mosin-Nagant rifle sight called the Konovalov type. This sight acts as both a tangent sight (for shorter ranges, marked as 4-12) and a ladder sight (for longer ranges, marked as 13-32). Note that the sight is sort of curved, as seen in the first image. Older Mosin Nagants have a flat shaped sight using the same idea.

The mistake that some people make is assume that these settings are in meters (e.g. 4 = 400 meters, 6 = 600 meters etc.) For Mosin-Nagants manufactured before 1930, this is not true -- in fact, these are calibrated in a unit called "Arshin" (plural: "Arshins" in English, "Arshiny" in Russian). So what the heck is an "Arshin" then?

To answer this question, we must go back to 16th century Russia, where this unit of length first originated. This unit was the Russian equivalent of the English "yard" measurement. Its actual length varied over the years, until Peter the Great standardized it in the 18th century to be about 27.95 inches long (or about 71.1 cm. or 0.78 yards). This continued to be how distances were measured in Russia until some time in 1925, when the Soviet Union officially adopted the metric system throughout the country. Konovalov type sights calibrated in arshins continued to be manufactured for some years after, until 1929.

Therefore, with older Mosin-Nagant rifles built before 1930, the sights were actually calibrated in arshins. Hence, when the slider is pushed to 4, the sights are set to aim at a distance of 400 arshins, not 400 meters. 400 arshins is approximately 285 meters, which explains why the rifle might not be shooting where the user expects it to!

Edit: The editor is indebted to Mr. Bernard Samartsev for his comments and corrections to the original article noted below.

Tuesday, August 13, 2013

The topic of today's study will be an unusual firearm, the Greener police shotgun.

The history of this unusual firearm dates back to shortly after World War I, when the British ruled over very large portions of the planet and the sun never set on the British empire. In several colonies around the globe, the British set up police forces employing locals to handle ordinary law and order issues, with British army garrisons to put down major rebellions and uprisings. There came a need to equip the local police forces of countries like Egypt, India, Hong Kong etc., with weapons to put down riots and jail escape attempts, without the need to involve the local army garrison. Therefore, the British government issued a specification for a new firearm for these police forces.

The requirements of this new firearm type were a bit unusual. First, many of these police forces were not well trained or educated, therefore the firearms had to be extremely simple, sturdy and reliable. They were expected to need minimal maintenance. Since there was a chance that the guns could be used against the British troops themselves, the guns had to be short-range weapons and single-shot only. Another request was that the cartridges used for these firearms should not be easily available. That way, if the police forces decided to rebel themselves, the British garrison could easily take them on.

Greener police shotgun. Click on image to enlarge.

With these requirements in mind, the firm of W.W. Greener, a well known manufacturer of firearms from Birmingham, UK, came up with the Greener police shotgun. The action chosen for this firearm was the Greener improved Martini action that we studied a couple of years ago. This reliable action was known for its simplicity and ruggedness. It was in the Martini-Henry rifle since 1871 and the Martini-Henry rifle was already used by many local militaries, which meant that many locals would be familiar with it. In addition, the barrel, springs and action were made of heavy-duty steel for extra strength and durability. The wood stock extended all the way to the end of the barrel, to prevent damage to the barrel. In addition, note the solid steel nose cap at the muzzle end of the barrel in the picture above. This cap served as extra protection for the end of the muzzle, so even if the gun was placed vertically with the muzzle-end on the floor, the steel cap kept the barrel about 1/4" off the floor. In addition, a bayonet could be attached to the steel cap. The butt-end of the stock also had a steel plate at the end, so it could be used as a club. The stock also had a compartment to store cleaning tools. The barrel of this shotgun had no rifling, so it could only be used as a short range weapon and since it used the Martini action, the user would have to manually unload and reload a new cartridge, each time he desired to fire it. The cartridge that this shotgun was designed to fire was a proprietary 14-gauge shell manufactured by Kynoch Ltd.

The original Mark-I model of this shotgun was released in 1921, mainly to colonial police forces in Egypt. However, it was soon discovered that unauthorized users could use a smaller commonly available 16-gauge cartridge in this gun and stuff the extra space with paper. In response to this, Greener released the Mark-III model shotgun, which had some improvements to prevent this:

New improved cartridge for the Greener Police Shotgun Mark III

In this newer model, the shotgun chamber was altered to take an unusual shaped cartridge. The base of the cartridge was the same diameter as a 12 gauge cartridge, but the front of it was narrowed down to 14 gauge. With an unusual bottle-necked cartridge shape like this, this cartridge could not be used with any other firearm.

In addition, the striker of the shotgun was also modified so that it could only be used with these unusual cartridges. Instead of a normal needle shaped striker, the new striker on this shotgun was shaped like a trident, with the outer two prongs longer than the middle prong. Note that the base of the new cartridge has a deep circular groove around the primer cap. The reason for this groove is so that the two outer prongs fit into the groove and the shorter middle prong can strike the primer of the cartridge. Therefore, the Mark-III shotgun could not use any other ammunition, except for this type of cartridge. If any other cartridge was used, the two longer outer prongs of the striker would strike the base of the cartridge first and prevent the shorter middle prong from striking the primer.

The end result of this was a cartridge that could not be used on any other firearm and a shotgun that could only fire a particular cartridge type. The British authorities were very careful to issue these cartridges in very limited numbers (about two or three per person). Therefore, if criminals stole these weapons or if the local government revolted, these guns would be useful only while the ammunition was available for them.

A lot of these shotguns were issued to colonial police forces in Egypt, Malaya, Hong Kong etc. Some of them were imported into the US in the 1930s, to be used in prisons. Greener continued to manufacture these shotguns even after British colonial rule ended in many parts of the world, until about 1975 or so. Used examples can be found on sale even today.